This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The TNC Microenvironment in the Development of Systemic Lupus Erythematosus. Thymic Nurse Cells (TNCs) have a major role in MHC restriction and the removal of apoptotic thymocytes. TNCs are severely depleted with disease onset and progression in systemic lupus erythematosus (SLE). The major goal of this study is to determine if the replacement of TNCs in the thymus of lupus mice will reduce or eliminate disease symptoms. In these studies thymic nurse cells were found to express the cytokeratins five and eight (K5 and K8) as well as the transcription factor 63 (Trp-63). The expression of Trp-63 is a characteristic of epithelial cell progenitors. This suggests that TNCs may have the potential to repopulate epithelial-free zones characteristic of the thymi of lupus-prone mice.